Control method and system

Abstract

The invention relates to a control method and system comprising an electronic control unit ( 11 ) controlling the electric current power supply from an electric power source to a motor-compressor arrangement ( 12, 13 ); the electronic control unit comprises a conversion means which is connected to an inversion means ( 15 ) to supply the voltage demanded by the motor ( 12 ). A PWM pulse width regulator ( 16 ) generates the switching signals for all the switching elements of the unit ( 11 ) relating to said demanded voltage.

1. A system for controlling an electric power supply from an electric power source which can be connected to an electric motor ( 12 ) through a control unit ( 11 ), wherein the electric motor ( 12 ) can in turn be connected to a compression means ( 13 ), said system comprising:
 means for detecting a voltage of the electric power source; 
 means for predetermining a desired operating speed of the electric motor ( 12 ); 
 means for calculating a voltage signal which must be applied to windings of the electric motor ( 12 ) to reach the predetermined desired operating speed; and 
 a PWM pulse width regulator ( 16 ) generating switching signals relating to the calculated voltage signal, to be applied to each of switching elements included in the control unit ( 11 ), so that the motor ( 12 ) reaches the desired operating speed, 
 wherein 
 the control unit ( 11 ) further includes energy conversion means ( 14 ) receiving energy from the electric power source, and 
 the energy conversion means ( 14 ) comprise a switching element which is in a permanent cutoff mode when the voltage level demanded by the electric motor ( 12 ) is lower than or equal to the voltage level of the electric power source and in a modulation mode when the voltage level demanded by the electric motor ( 12 ) is greater than the voltage level of the electric power source. 
 
     
     
       2. A system according to  claim 1 , wherein
 the energy conversion means ( 14 ) is a boost converter, 
 the control unit ( 11 ) further includes three-phase inversion means ( 15 ) connected to the energy conversion means ( 14 ) which is in turn connected to the electric motor-compressor assembly ( 12 ,  13 ), and 
 each switching element of the three-phase inversion means ( 15 ) works in permanent conduction and in cutoff when the voltage of the electric motor ( 12 ) is greater than the voltage of the electric power source and works in modulation and in cutoff when the voltage of the electric motor ( 12 ) is less than or equal to the voltage level of the electric power source.